The collection of solar energy for heating and the generation of power involves the radiation of sunlight onto conduits and power generating cells; conduits transporting a heat transfer media and/or energy converters that directly produce electrical power. Solar quantity or concentration becomes a primary consideration for the impingement of light rays onto said collector tubes or converters, and heretofore the white light of the sun rays has been concentrated for so-called high temperature heat collection or conversion. However, it is known that the longer "red" (infrared) rays of light are those which have the greater heating effect, while the shorter "violet" or "ultraviolet" rays have the lesser heating effect and are required, for example in photovotaic power generation. Furthermore, when considering photovoltaic power generation, only high energy photons (some 45% of the solar radiation) will be effective, ie the ultraviolet and some of the visible spectrum, but not the infrared. Also, those invisible infrared rays just beyond the "red" of the visible spectrum have known penetrating heating effect. Therefore, it is a general object of this invention to advantageously employ either or both of those rays, namely infrared and ultraviolet at opposite ends of the spectrum, and of the sun which are known to have said effects, in preference to those rays that do not; and to this end dispersion is employed to break sunlight into its parts which are then selectively focused upon a target collector or converter as circumstances require.
The prism is a solid transparent body that refracts light, and strictly speaking is a solid figure with ends of equal size and shape in parallel relation and whose sides extending therebetween are parallelograms. The most common prism is a triangular solid of glass or the like, for refracting and dispersing light into and beyond the visible spectrum ranging from infrared heat rays to the power generating ultraviolet rays. Dispersion in the prism is by means of refraction or the bending of light rays as they pass obliquely from one medium (air) to the other (glass or plastic) or different density in which its speed changes; a phenomenon thereby breaking the light into its constituent parts represented by the bands of the spectrum. It is an object therefore to advantageously employ said prismatic phenomenon and concentrate therefrom a range of heat rays which is most practical as may be required for application to the target collector or converter.
The selection of heat rays involves an alignment with that portion of the spectrum both visible and invisible, and the projection of that portion upon the collector or converter. The projection of selected heat rays can be direct or concentrated and at a 1 to 1 ratio or at a concentration ratio for developing commensurately high temperature or energy at the target. That is, direct projection is suitable for low temperature-low power operations, while concentrated projection is necessary for high temperature-high power operations. It is an object therefore to concentrate that portion of the spectrum selected for heating and to project it exclusively. As stated above, the dispersion is by means of a prismatic solid which refracts bands of light along angularly divergent "focal lines or planes". Accordingly, a linear lens having a focal line or plane is aligned with the median focal plane of the selected spectrum portion emitting from the prism to project the same to the target collector or converter also of linear form at the point of focus. In practice, a linear Fresnel lens is used for this projection.
Tracking of the sum in its traverse between horizons is either by bodily movement of the apparatus herein disclosed or preferably by turning of the prism disclosed in a plane substantially normal to the sun in its movement across the sky. In practice, a clock drive more specifically referred to as an "astro timer" is employed to revolve the prism in order to maintain substantial alignment of the aforesaid "focal plane" of the prism and lens projection respectively. Nominal operational time periods are accommodated by revolvement of the prism alone, while extended operational time periods are accommodated by combining therewith a reflective mirror that also moves with the astro timer or clock drive to track the selected spectrum onto the target. A feature is the use of an array of prismatic projection units and each with its prism and mirror articulated to concentrate the selected spectrum onto the target collector or converter for high heat and/or power operation. In practice therefore, each mirror has its angular adjustment to the target, and the distance to the target from each prism unit is accommodated by the focal length of its projection lens or a collection lens.
The optics of the collector prism is critical, with the apex B uppermost and the quadralateral faces AB and CB active to refractively pass sunlight so as to disperse the same into the utilitarian spectrum, especially the heat portion thereof. In accordance with this invention the lowermost quadralateral face AC is inactive and in practice is frosted so as to be non-reflective. Accordingly, a feature is the reduction of internal reflection within said prism by maintaining substantial normality of the face AB to the solar source rays and by careful selection of the acute angle at the apex B. Therefore, the critical angle of the prism is at the apex B, and the optimum of which has been found to be approximately 36.degree. based on an air to glass interface and which varies as a function of the respective indicies of refraction, for the substantial elimination of internal reflection and for the purpose of conducting the tracking function through a wide range, and especially in combination with a mirror M that contra rotates therewith at a ratio of 1 to 2. That is, the mirror rotation is 1.degree. to 2.degree. of prism rotation. The relatively small apex angle of the prism operates in conjunction with the tracking mirror without the former blocking light, especially in the heat spectrum portion, from the latter.
The heat collector and/or power converter can vary in form and in construction, however it is disposed linearly along the focus of the at least one prismatic-lens collector above referred to. A feature of this invention is the conservation of concentrated heat in the collector or converter at the point of focus, and which is structurally compact while the collecting prism and tracking mirror are structurally expansive. In practice, the said collector or converter is encased within a transparent tube, preferably vacuumized, for the substantially complete absorption of energy from the heat rays impinging thereupon. A condensing reflector backs up the target to return the heat rays that are or may be dispersed to initially pass thereby.